The present invention is directed to an explosive powder charge operated fastening element driving tool including a housing with a handle projecting from its rear end. A firing mechanism having a cocking spring is located in the rear part of the housing with a muzzle part having a non-circular circumferential contour at its front part projecting in the firing direction out of the front end of the housing. The muzzle part is displaceable in the firing direction relative to the housing against retaining stops and displaceable in the opposite direction against stopping means. A contact pressure sensor is displaceably mounted relative to the muzzle part so that it can be displaced into a position for compressing the cocking spring whereby the tool is in the ready-to-fire condition. When the muzzle part is displaced in the rearward direction, the forward end of the contact pressure sensor is flush with the front end of the muzzle part and the driving tool is ready to be fired.
Nails or similar fastening members are driven at high speed into a hard receiving material, such as concrete or steel, by means of an explosive powder charge operated fastening member driving tools. For safety reasons, such driving tools incorporate contact pressure members which permit the firing of the driving tool only when the front end of its muzzle part is pressed against the surface of the receiving material.
In a driving tool, as disclosed in DE-AS No. 16 03 841, the contact pressure member is a tube-shaped contact pressure sensor displaceably supported in the muzzle part. When the driving tool is not in the firing condition, the sensor projects forwardly in the driving direction beyond the front end face of the muzzle part. The muzzle part has a central bore concentric with the driving axis. A guide bushing or barrel for a drive piston contacts the rear end face of the contact sensor and the barrel is biased in the driving or firing direction by a cocking spring in a firing mechanism. The barrel is displaceably supported in a housing and when the sensor is pressed rearwardly, it biases the barrel in the rearward direction which, in turn, compresses the cocking spring into the ready-to-fire condition.
The muzzle part is supported in the housing so that it can be displaced in the axial direction to a limited extent, but is not rotatable. To limit the movement of the muzzle part in the driving direction, retaining stops are provided to contact one another and to limit the movement in the opposite direction, stop means cooperate with one another which are provided on the muzzle part and on the housing. The installation of the muzzle part in the specific rotational position requires auxiliary tools and considerable installation effort. Accordingly, the removal and replacement of the muzzle part for changing the driving piston, is very cumbersome.
Driving fastening members into narrow rail sections or the placement of such members near or along a wall, requires a non-circular circumferential contour of the muzzle adjacent to its front end. A handle extending sidewise from the housing is in a specific rotational position relative to the non-circular muzzle portion.
Such an arrangement frequently results in handling problems when the driving tool is used, with the handle located so close to the wall when the driving operation is carried out, that satisfactory gripping of the handle and effective guidance of the driving tool is not possible.